In a power transmitting apparatus that transmits power from an engine of a vehicle, such as an automobile, to its wheels, it is necessary not only to transmit the power from the engine to the wheels, but to allow radial and axial displacements as well as moment displacements from the wheels caused by bounds or turns of the vehicle during running on a rough road. Accordingly, the power transmitting apparatus is connected to the driving wheel via a wheel bearing apparatus that includes a constant velocity universal joint. One end of a drive shaft arranged, between an engine side and the driving wheel side, is connected to a differential gear unit via a constant velocity universal joint of a sliding type. The other end of the drive shaft is connected via a secured type constant velocity universal joint.
Various types of wheel bearing apparatus have been previously proposed, for example, as shown in FIG. 5. The wheel bearing apparatus 50 includes a wheel hub 51 that mounts a wheel (not shown). A double row rolling bearing 52 rotatably supports the wheel hub 51. A secured type constant velocity universal joint 53, for transmitting power of a drive shaft (not shown), is secured with the to the wheel hub 51.
The wheel hub 51 is integrally formed at one end with a wheel mounting flange 54 to mount a wheel. The wheel hub outer circumference includes one inner raceway surface 51a. A cylindrical portion 51b axially extends from the inner raceway surface 51a. The double row rolling bearing 52 includes an outer member 55 and an inner member 57. The outer member 55 is integrally formed with a body mounting flange 55b to be mounted on a suspension apparatus (not shown). The outer member inner circumference is formed with double row outer raceway surfaces 55a, 55a. The inner member 57 is inserted into the outer member 55, via double row balls 56, 56.
The inner member 57 includes the wheel hub 51. An inner ring 58 is inserted onto the cylindrical portion 51b of the wheel hub 51. The inner ring outer circumference includes the other inner raceway surface 58a. The inner ring 58 is axially secured relative to the wheel hub 51 by a caulked portion 51c. The caulked portion is formed by plastically radially outwardly deforming an end of the cylindrical portion 51b of the wheel hub 51.
The constant velocity universal joint 53 includes an outer joint member 62 including an integrally formed cup shaped mouth portion 59. A shoulder portion 60 forms a bottom of the mouth portion 59. A shaft portion 61 axially extends from the shoulder portion 60. The outer joint member 62 is inserted into the wheel hub 51 in a torque transmittable fashion. A female serration 63 is formed on the inner circumference of the wheel hub 51. A male serration 64 is formed on the outer circumference of a shaft portion 61 of the outer joint member 62. The female and male serrations 63, 64 are mated with each other. The shaft portion 61 is fit into the wheel hub 51 until the shoulder portion 60 abuts against the caulked portion 51c of the wheel hub 51. Finally, a securing nut 66 is fastened onto an outer thread 65, formed on an end of the shaft portion 61, by a predetermined fastening torque to axially separably connect the wheel hub 51 and the outer joint member 62.
It is known that a large torque is transmitted from an engine to a wheel, via a sliding type constant velocity universal joint (not shown), during a low engine speed range such as during starting of a vehicle. Thus, a torsional deformation is caused in the drive shaft. As a result, torsional deformation is also caused in the inner ring 57 of the double row rolling bearing 52 that supports the drive shaft. When a large torsional deformation is caused in the drive shaft, a so-called “stick-slip noise” is generated by a sudden slip between abutting surfaces of the outer joint member 62 and the inner member 57.
To cope with this problem in the prior art wheel bearing apparatus 50, the caulked portion 51c of the wheel hub 51, against which the shoulder portion 60 of the outer joint member 62 abuts, is formed as a flat surface. A circular recessed groove 67 is formed on the flat surface of the caulked portion 51c at a radially middle portion of the flat surface, as shown in FIG. 6. The groove 67 is filled with grease. This makes it possible to reduce the surface pressure applied to the caulked portion 51c by a fastening force of the securing nut 66. Accordingly, it is possible to prevent plastic deformation of the caulked portion 51c and loosening of the securing nut 66 and to reduce the coefficient of friction of the abutted surfaces owing to the grease. Thus, it is possible to reduce frictional energy at the abutted surfaces and to prevent the generation of the stick-slip noise that is caused by a sudden slip at the abutted surfaces between the shoulder portion 60 and the caulked portion 51c. Reference Patent Document 1: Japanese Laid-open Patent Publication No. 136908/2003
However, in the prior art wheel bearing apparatus, an additional machining step is required to form the recessed groove 67 on the flat surface of the caulked portion 51c. Thus, it is believed that it would not only increase the manufacturing cost but reduce the strength of the caulked portion 51c. In addition, grease contained in the recessed groove 67 of the caulked portion 51c tends to leak out during running of the vehicle. Thus, it is difficult to prevent the generation of a stick-slip noise for a long term.